MCSDs are commonly used to assist the pumping action of a failing heart. Typically, an MCSD includes an implantable blood pump that is surgically implanted in the patient's body. The MCSD has a housing with an inlet and an outlet and has a rotor mounted within the housing. The inlet of the housing is connected to a chamber of the patient's heart, typically the left ventricle, whereas the outlet is connected to an artery such as the aorta. Rotation of the rotor drives the blood from the inlet towards the outlet and thus assists flow from the chamber of the heart into the artery.
Blood pumps used in MCSDs desirably are provided with contactless bearings so that, in operation, the rotor floats within the housing. With contactless bearings, there is no solid-to-solid contact between the rotor and the housing and thus no mechanical wear during operation. One form of contactless bearing is a hydrodynamic bearing. As further discussed below, in a hydrodynamic bearing, the liquid being pumped passes between a surface of the rotor and a surface of the clearance between the surfaces of a hydrodynamic bearing is many times larger than the dimensions of blood cells. However, in some cases the blood passing through the pump may contain particles of thrombus, a solid or semi-solid deposit generated within the patient's body. The thrombus can lodge on a surface of the hydrodynamic bearing and impede its operation. The surfaces are configured so that as the rotor turns, the fluid disposed between these surfaces exerts pressure on the surface of the rotor that holds the rotor away from the housing.